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Aluminium oxide is used for its hardness and strength. Its naturally occurring form, corundum, is a 9 on the Mohs scale of mineral hardness (just below diamond). It is widely used as an abrasive, including as a much less expensive substitute for industrial diamond. Many types of sandpaper use aluminium oxide crystals.
Aluminium(I) oxide (Al 2 O) Aluminium(II) oxide ( AlO ) (aluminium monoxide) Aluminium(III) oxide (aluminium oxide), ( Al 2 O 3 ), the most common form of aluminium oxide, occurring on the surface of aluminium and also in crystalline form as corundum , sapphire , and ruby .
The melting point of aluminium oxide is 2050°C (2323K), much higher than pure aluminium's 658°C (931K). [6] This and the insulativity of aluminium oxide can make welding more difficult. In typical commercial aluminium anodizing processes, the aluminium oxide is grown down into the surface and out from the surface by equal amounts. [7]
Nanoscale oxide due to the small diameter of the particles/fibers, high specific surface area and activity associated with the defects, and the specific structure of the nanoparticles (the volume and size of pores, degree of crystallinity, phase composition, structure, and composition of the surface) strongly enhances the catalytic properties ...
The names aluminium and aluminum are derived from the word alumine, an obsolete term for alumina, [j] the primary naturally occurring oxide of aluminium. [119] Alumine was borrowed from French, which in turn derived it from alumen , the classical Latin name for alum , the mineral from which it was collected. [ 120 ]
although the aluminium species in solution is probably instead the hydrated tetrahydroxoaluminate anion, [Al(OH) 4] − or [Al(H 2 O) 2 (OH) 4] −. [2] Oxidizing acids do not effectively attack high-purity aluminium because the oxide layer forms and protects the metal; aqua regia will nevertheless dissolve aluminium.